Identifier

Author

Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

The compact mesocosm which was designed for a laboratory scale was used for the kinetic study of refractory organic compounds in a tidally influenced coastal marsh wetland soil. The tidal cycles were controlled pneumatically using an air chamber inside the mesocosm tank. Phenanthrene as the test compound showed that its degradation in the intertidal wetland soil was faster than that in the subtidal wetland soil. Oxygen resupply during the tidal cycles to the intertidal wetland soil would enhance the degradation. Comparison of degradation rates of phenanthrene (Phe), pyrene (Pyr), and benzo[e]pyrene (BeP) were also studied using the mesocosm. The degradation rates of Phe, Pyr, and BeP (3.42, 3.11, and 2.50%/day, respectively) in the intertidal wetland soil are significantly different from the degradation rates of Phe, Pyr, and BeP (2.12, 1.81, and 1.20%/day, respectively) in the subtidal wetland soil. BeP stays longer in the wetland soil and is more persistent than the other two compounds as its molecular weight is higher than that of Phe and Pyr and its water solubility is lower than that of Phe and Pyr. The effect of nutrient addition to the wetland soil to enhance the degradations also was examined. Inorganic nitrogen (N) and phosphorus (P) were added to the contaminated wetland soil with C:N:P ratio of 100:10:3 (C was on the organic compounds added, not including what was already in the soil). The statistical combination model of compounds, depths, and nutrients was tested to see the effects on the PAH degradation rates. There were significant differences of degradation rates among the three compounds and between the depths, but no significant effect of the nutrient addition to the sediments. The statistical difference of the PAH degradation rates due to the nutrient addition which was 0.10 % day-1 (P<0.05) was significantly zero. The nutrition added functioned well only in the beginning and then it leached to the water and flushed out. The designed mesocosm has been a useful tool for a complementary study of non-volatile refractory organic compounds in coastal wetland soil.